This invention relates to a process for the preparation of alkyl aryl sulfonate compositions, and more particularly to the preparation of concentrated sulfonate compositions of low viscosity.
Alkyl aryl sulfonates are known materials, recognized for their valuable solvent and surface active properties in a variety of applications. As an example, they have been recommended for use in various detergent formulations. Moreover, because of chemical and thermal stability, they have proved to be particularly attractive for use in various enhanced oil recovery processes. U.S. Pat. Nos. 3,799,263, 3,861,466, 4,022,699 and the commonly-assigned, copending application Ser. No. 560,468, filed Dec. 12, 1983, for instance, describe the use of alkyl xylene sulfonates in oil recovery services.
One drawback to the conventional use of alkyl aryl sulfonates in all such applications is the high viscosity which has been characteristic of the sulfonates in concentrated form. The sulfonates of interest are conventionally prepared by reacting one or more alkyl aryl hydrocarbons with, for example, sulfur trioxide or fuming sulfuric acid to first produce alkyl aryl sulfonic acid. When these acids are then neutralized to yield the sulfonate salts, the thick, paste-like consistency of the product gives rise to problems in transportation, storage, and formulation.
It is known to be possible to dilute the sulfonate salts thus produced to lower their viscosity and improve their handling characteristics. However, this has entailed the inclusion in the product of a substantial amount of a diluent. The need for diluent often represents an added material cost. Moreover, and often more importantly, there is an added cost associated with transporting and storing the larger quantities of diluted sulfonate mixture. These factors are of particular significance when the alkyl aryl sulfonates are applied to oil recovery service. In many cases, the remote location of the oil production site increases the difficulty and expense of transportation and storage. Although the sulfonates are necessarily diluted before use, suitable diluents (e.g., brine and oil) are readily available at, and need not be transported to, the production site. In fact, the recovery process typically call for the injection into the oil-bearing formation of a dilute (e.g., 1% by weight) solution of alkyl aryl sulfonate in brine, or for the injection of a sulfonate and oil mixture into a reservoir prior to water-flooding.
Accordingly, it is a principal object of this invention to provide a method for preparing alkyl aryl sulfonate compositions of low viscosity. It is a further object to accomplish this in a way which maintains the products as concentrates and which, in particular, does not depend upon the inclusion of large proportions of oils, water or other diluents.
In part, the present invention accomplishes these objects by incorporating a lower aliphatic alcohol into the desired sulfonate product at a critical stage of sulfonate preparation. There are teachings in the prior art of alkyl aryl sulfonate compositions containing lower aliphatic alcohols. For instance, L. W. Holm in the aforementioned U.S. Pat. No. 4,022,699, U.S. Pat. No. 3,769,209, and also in Canadian Pat. No. 1,011,215 discloses alkyl aryl sulfonate compositions containing alcohols which act as stabilizing agents, rendering the sulfonate more effective and enhancing the properties of microemulsions formed from the compositions during oil recovery applications. However, no criticality is suggested by these patents for the order of processing steps utilizing in the preparation of the alkyl aryl sulfonates. Moreover, the compositions described in these patents contain substantial amounts of oils which act as diluents for the sulfonate concentrates.